I am facing CPU high load issue with the server. Server hardware and software details are as follows. CPU load is continuously above 35. Daily site visitor is 18000. So I am planning to MySQL performance tuning. Please suggest me on the same.

What exactly is your problem? You're running a server, but you're also using that same server to run Dolphin, correct? That CPU load looks average for running Dolphin and whatever your server is doing. Dolphin normally only uses two major threads for the bulk of its emulation, so if those two monopolized two of your eight cores, your CPU usage should be around 25%. Dolphin also has additional minor threads (input, GUI rendering, etc) that would also consume a few more percentage points of CPU usage. Whatever your server is doing is bound to affect CPU usage as well. 35% sounds pretty average.

You did, however say that it goes above 35%. Some specific numbers would be nice to look at. It shouldn't be that hard for your server to give you a graph of CPU usage over time. At any rate, why is the CPU usage a problem? Is running a server affecting your Dolphin gameplay? Is gaming on Dolphin affecting your server? In either case the solution is simple: use different machines for either task.